I was just wondering what a THERMAL VACUUM SWITCH does. I am supposed to have one screwed in to the top of the thermostat houseing but instead of the switch i have a big blue blob of silicon blocking the hole. How important is this switch?
A TVS switches vacuum from one place to another based on the temperature of the thing it's mounted on. They're pretty common in vacuum-based emissions systems, like on the '82-'90 CJs and YJs, and probably lots of other vehicles.
Most times they're used for doing things like purging the charcoal canister after the engine has warmed up. There should be at least two tubes sticking out of it: one will go to a vacuum source (carb or intake manifold), and the others will go someplace else. Is there a sticker under the hood somewhere with the vehicle's vacuum diagram on it?